Multi-Region ASP.NET Core Session Provider [Deprecated]

NCache Multi-Region ASP.NET Core Session Provider enables efficient session sharing across geographical data centers via Location Affinity. By replicating only session metadata across a WAN, it ensures high availability and disaster recovery without high bandwidth expenses, allowing users to maintain session state even if traffic is rerouted to a different region.

Multi-Region ASP.NET Core Session Provider for NCache

Figure 1: Session Sharing across Data Centers

To share ASP.NET Core sessions across regions, you need to enable Location Affinity. This is enabled by setting the EnableLocationAffinity flag to true and providing the cache names and prefixes to identify the source (location) of the cache for the request. You can provide multiple cache names that form the web farm. However, the cache specified against CacheName is considered the primary cache by default.

Prerequisites

Before using the ASP.NET Core Multi-Region Sessions with NCache, ensure that the following prerequisites are fulfilled:

Step 1: Initialize Multi-region Session Services

The session management service needs to be initialized. In Startup.cs, use the AddNCacheSession extension method on IServiceCollection in ConfigureServices() to initialize the service. The very basic overload of this extension method takes an IOptions<NCacheSessionConfiguration> as its base configuration.

There are two methods to specify configurations:

  1. Through your application Startup.cs.
  2. In JSON format in appsettings.json.

Method 1: Specifying Configurations in Startup.cs

To enable session sharing, it is required to set the EnableLocationAffinity flag to true and provide the list of caches in AffinityMapping. Note that one of the caches should match the CacheName, which is considered the primary cache. It is also required to specify a directory that is shared by both applications.

Note

The cache prefix should be a maximum of 4 characters long.

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services
    services.AddMvc();
    services.AddDataProtection()
    .PersistKeysToFileSystem(new DirectoryInfo(dir))
    .SetApplicationName("SharedCookieApp");

    services.AddNCacheSession(configuration =>
    {
        configuration.CacheName = "LondonCache"; // compulsory
        configuration.EnableLogs = true;
        configuration.SessionOptions.IdleTimeout = 5;
        configuration.EnableLocationAffinity = true;
        configuration.AffinityMapping = new CacheAffinity[]
        {
            new CacheAffinity { CacheName = "LondonCache", CachePrefix = "LDNC"},
            new CacheAffinity { CacheName = "NewYorkCache", CachePrefix = "NYKC"},
            new CacheAffinity { CacheName = "TokyoCache", CachePrefix = "TKYC"},
        };
    });
}
Note

To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Method 2: Specifying Configurations in appsettings.json

The session management service needs to be initialized. In Startup.cs, use the AddNCacheSession extension method on IServiceCollection in ConfigureServices() to initialize the service. The very basic overload of this extension method takes an IOptions<NCacheSessionConfiguration> as its base configuration.

Note

The cache prefix should be a maximum of 4 characters long.

"NCacheSettings": {
    "EnableLocationAffinity": true,
    "EnableLogs": true,
    "RequestTimeout": 5,
    "CacheName": "LondonCache",
    "AffinityMapping": [
      {
        "CacheName": "LondonCache",
        "CachePrefix": "LDNC"
      },
      {
        "CacheName": "NewYorkCache",
        "CachePrefix": "NYKC"
      },
      {
        "CacheName": "TokyoCache",
        "CachePrefix": "TKYC"
      }
    ]
}

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services
    services.AddMvc();

    // Add services to the container                    
    services.AddNCacheSession(Configuration.GetSection("NCacheSettings"));
}

Step 2: Configure HTTP Request Pipeline Middleware

Once the services have been initialized, you can configure the HTTP request pipeline by adding middleware in the Configure method. The following is an excerpt showing the addition of a middleware layer through the use of the UseNCacheSession extension method in IApplicationBuilder. The NCache session middleware should always be placed before any middleware that uses sessions.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    if (env.IsDevelopment()){
        app.UseDeveloperExceptionPage();
        app.UseBrowserLink();
    }
    else{
        app.UseExceptionHandler("/Home/Error");
    }

    app.UseStaticFiles();

    app.UseNCacheSession(); // Store NCache session data

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=myApp}/{action=Index}/{id?}");
    });
}

Additional Resources

NCache provides a sample application for Session Caching on GitHub.

See Also

.NET: Alachisoft.NCache.Web.SessionState namespace.